Conventional electrical interconnect and switching technology is rapidly becoming a critical issue in the realization of systems using high speed silicon and GaAs - based technologies. Comparisons between optical interconnect techniques and conventional electrical interconnect techniques are made as they are applied to high speed electronic computing systems. Theoretical and empirical data are used to identify the advantages of optical interconnects at various levels. Besides the inherent advantages of optics such as speed, reduced electromagnetic and radio frequency interference and crosstalk, optical interconnects are capable of providing larger fanouts at higher bandwidths, with possible lower system power and complexity. In addition, optics has an advantage over conventional interconnects via the density potential of free-space interconnects. A review of recent analysis and results of using optical communication in high speed electronic computing applications is presented.
Optical interconnection offers improved performance of VLSI circuits and systems. Planar optical waveguides allow interconnections to be printed directly onto optical circuit boards. The experimental assessment of waveguide options is discussed. Combinations of waveguide bends and intersections have been modelled, and experimental results are given.
We describe a new integrated optics structure achieved on silicon substrate by chemical vapor deposition of silica. That structure allows the realization of integrated optical circuit very attractive in the field of optical communications (multiplexer and demultiplexer, couplers...) but also in the new field of optical interconnects.
Soliton beams propagate in homogeneous nonlinear Kerr materials, staying confined in a self-induced waveguide, under strong and suitably shaped laser illumination. Interaction of two soliton beams will be presented as a new physical tool for high speed, optically driven single mode interconnections.
Fabrication processes of passive ion-exchanged glass waveguide components for optical interconnections are described. These processes are based on the use of either Ag thin-film sources or potassium ionic masking for Aq+-Na+ exchange with a molten salt source. Emphasis is put on the controllability and versatility of waveguide profiles.
We analyse optical solutions to realize crossbar networks in which connected users can send and receive information with all the others. Transmitters, receivers and links are now on the shelf. However optical switches have been the most critical point. A large variety of them are studied or developped. They can be packed into three groups : commutators, deflectors and directional couplers. The main characteristics of these devices are the attenuation, the crosstalk and the rise time. We analyse the main network parameters which are the number of processors, the reconfiguration time and the data rate.
Increasing complexity and processing speed of electronic circuits and a high device density have led to serious problems in electrical interconnections. Their limitations arise from their signal transmission capacity. power consumption. crosstalk. and reliability. Optical links may solve such problems by offering high data rates of several gigabits per second. large fanouts of up to 100 loads. good reliability and less power expenditure. Optical fibers, integrated optical waveguides or free-space transmission links may be applicable. For the free-space links, lenses. mirrors and holograms can be used to guide the light waves. In this paper, reconfigurable optical interconnection schemes are proposed and described which are based on optoelectronic holograms. Their interference patterns can be changed dynamically. To establish connections as free-space links, the light beams emitted from even hundreds of light sources are imaged onto an array of small dynamic holograms. Their interference patterns are optically and electronically controllable. These holograms diffract and focus each of the incident light beams individually onto the receiving photo-diodes. By changing the hologram interference patterns dynamically. an optical switch is obtained. It renders the establishment of reconfigurable optical interconnections. As optoelectronic holograms very-high-resolution spatial light modulators are proposed.
Expressions for the effective radius, angular aperture, numerical aperture and f-number are determined for a general GRIN lens with axial and radial variation of the index profile. Obtained results are applied to the particular case of Selfoc lens and positive and negative conical index profile.
The capability of optics to face the new demand in advanced computer technology is evaluated. The attention is not restricted to passive interconnections, fixed or programmable, but rather emphasizes the active control requirements for optical network nodes and parallel data handling. All-optical computing research is also considered, for its ability to implement logic blocks and data-driven processing inside the parallel architecture of modern electronic array processors or inference machines.
Wavelength multiplexing (WDM) offers enormous potential for increasing the information capacity of an optical fiber. The use of WDM also decreases the requirea number of fibers (and interconnections) in an optical bus structure. Some of the different existing methods of design and fabrication of MUX-DEMUX devices are shortly reviewed, and experimental results are presented referring to a guided-wave geodesic multiplexer. The problems of interconnecting optical fibers to a thin-film waveguide are also discussed.
An electromechanical optical scanner is described, which, allows the sequential coupling. of a single to 19 multimode optical fibers. In order to achieve a good. coupling efficiency between the fibers, quarter pitch graded index microlenses (GRIN) are used. Technical data of the system and the evaluation of the insertion, losses are presented, along with loss and repeatability measurements for each channel.
Focal Shift and Relative Focal Shift in a GRIN lens are evaluated when it is illuminated by a Gaussian beam. An equivalent Fresnel Number is stablished. The influence in interconnections is studied when gaussian sources and ultrashort focals are considered. The obtained results are applied to Selfoc lenses.
Based upon the scalar diffraction theory we have derived a very simple condition to control the optimization in the coupling phenomenon in a holocoupler - optical fiber system. A systematic numerical procedure allows a scanning simulation at the output plane of the system. The influence of the physical optimization parameters can be easily obtained giving an interesting criterium for the optimization of the output signal in a suitable experimental set up.
Optical interconnections represent a powerful answer for the foreseen speed requirements and complex parallel circuit architectures. The flexibility in connection design and the non interfering character, inherent to optical beam carrier makes it very attractive to examine the major problems on the application of various types of optical interconnections. Holographic techniques have been proved capable to respond to the implementation of optical fibre interconnections with pre-established performances. Sophistication can range from back-to-back, low tolerance couplers, to multiplexers and demultiplexers. Switching devices can also be implemented while programmable and reconfigurable, real-time interconnections are been researched. The comparative advantages in performance and the uniqueness of solution to known critical limitations in the progressively complex interconnection problems, in particular, on advance micro-optoelectronics made holographic coupling to regain a central interest in multiple situations of optical interconnecting. A short state-of-the-art review on devices and prospects will be given stressing applications and potentialities to be explored, in optical circuitry.
Photothermoplastic devices with recyclability of 10,000 cycles and diffraction efficiency of 20 % at 633 nm have been developed. These performances arise mainly from a chemical stabilization of the thermoplastic and from the use of layers thickness showing reduced corona charging damage.
The connection of two optical fibers is a problem of great interest in all the application areas of fiber optic laser systems.It has been widely investigated in the field of optical communications,where low power laser diodes are usually employed.Less attention has been devoted so far to the problem of fiber interconnections with medium and high power laser sources,which are used for instance in the industrial and medical fields. We have analysed the possibility of using lens ended fibers to improve the performances of conventional connections,through the relaxation of the positional tolerances.Two types of connections (a) bulb ended fiber to flat ended fiber ; (b) bulb ended fiber to bulb ended fiber are considered,in the case of eaual fibers as well as in the case of fibers with equal core diameter and different N.A. These new connections have been experimentally tested,and their performances compared with usual flat-flat connection.It has been shown that bulb ended fiber connections constitute an effective improvement with respect to the conventional ones.